2.Mech - IJMPERD - Linear Static - P.v.K

LINEAR STATIC STRUCTURAL ANALYSIS OF OPTIMIZED PISTON FOR BIO-FUEL

USING ANSYS

CH. VENKATA RAJAM1, P. V. K. MURTHY

2 & M. V. S. MURALI KRISHNA

3

1Mechanical Engineering Department, CVSR College of Engineering, Ghatkesar, Hyderabad, Andhra Pradesh, India

2JayaPrakash Narayan Educational Sciety Group of Institutions, Mahabubnagar, Andhra Pradesh, India

3Mechanical Engineering Department, Chaitanya Bharathi Institute of Technology, Gandipet, Hyderabad,

Andhra Pradesh, India

ABSTRACT

An optimized piston which is lighter and stronger is coated with zirconium for bio-fuel. The low grade LHR

engines are using ceramic coatings on piston, liner and cylinder head, while medium grade LHR engines provide air gap in

the piston and other components. It is necessary to test the coated piston for withstanding the stresses and strains. In this

paper, the coated piston undergone a vonmisses test by using ANSYS for load applied on the top. Analysis of the stress

distribution was done on various parts of the coated piston for finding the stresses due to the gas pressure and thermal

variations. Vonmisses stress is increased by 16% and deflection is increased after optimization. But all the parameters are

well with in design consideration.

KEYWORDS: ANSYS, Vonmisses Stress, Linear Analysis, Zirconium Coating

INTRODUCTION

Automobile components are in great demand these days because of increased use of automobiles. The increased

demand is due to improved performance and reduced cost of these components. R&D and testing engineers should develop

critical components in shortest possible time to minimize launch time for new products. This necessitates understanding of

new technologies and quick absorption in the development of new products [1].

A piston is a moving component that is contained by a cylinder and is made gas-tight by piston rings. In an engine

its purpose is to transfer from expanding gas in the cylinder to the crank shaft via piston rod and or connecting rod. As an

important part in an engine piston endures the cyclic gas pressure and inertia forces at work and this working condition

may cause the fatigue damage of the piston. The investigations indicate that greatest stress appears on the upper end of the

piston and stress concentration is one of the mainly reason for fatigue failure [2].

The piston is designed for LHR engines for bio-fuel. The vegetable oils are promising substitutes for diesel fuel as

they are renewable in nature. The vegetable oils have the problems of high viscosity, low volatility and their

polyunsaturated character. Hence crude vegetable oil was converted into biodiesel by treating crude vegetable oil was

stirred with methanol at around 60-70oC with 0.5% of NaOH based on weight of the oil, for about 3 hours. At the end of

the reaction, excess methanol is removed by distillation and glycerol, which separates out was removed. The methyl esters

were treated with dilute acid to neutralize the alkali and then washed to get free of acid, dried and distilled to get pure

vegetable oil esters or biodiesel. The drawbacks associated with vegetable oils and biodiesels for use in diesel engines call

for LHR engines. The concept of LHR engine is to reduce heat loss to coolant by providing thermal insulation in the path

of heat flow to the coolant. LHR engines are classified depending on degree of insulation such as low grade, medium grade

International Journal of Mechanical and Production

Engineering Research and Development (IJMPERD)

ISSN 2249-6890

Vol. 3, Issue 2, Jun 2013, 11-20

© TJPRC Pvt. Ltd.

12 Ch. Venkata Rajam, P. V. K. Murthy & M. V. S. Murali Krishna

and high grade insulated engines. Several methods adopted for achieving low grade LHR engines are using ceramic

coatings on piston, liner and cylinder head, while medium grade LHR engines provide air gap in the piston and other

components with low-thermal conductivity materials like Superni, cast iron and mild steel etc and high grade LHR engine

is the combination of low grade and medium grade engines. To create hot combustion chamber ceramic coating of 500

microns given on the crown of the aluminum piston by plasma spray technique [3].

A linear FEA analysis is undertaken when a structure is expected to behave linearly, i.e. obeys Hook’s Law. The

stress is proportional to the strain, and the structure will return to its original configuration once the load has been removed.

A structure is a load bearing member and can normally be classified as a bar, beam, column, or shaft [4].

MODELLING

Optimized Piston Design

The piston is designed according to the procedure and specification which are given in machine design and data

hand books. The dimensions are calculated in terms of SI Units. The pressure applied on piston head, temperatures of

various areas of the piston, heat flow, stresses, strains, length, diameter of piston and hole, thicknesses, etc., parameters are

taken into consideration.

Design Considerations for a Piston

In designing a piston for an engine, the following points should be taken into consideration:

• It should have enormous strength to withstand the high pressure.

• It should have minimum weight to withstand the inertia forces.

• It should form effective oil sealing in the cylinder.

• It should provide sufficient bearing area to prevent undue wear.

• It should have high speed reciprocation without noise.

• It should be of sufficient rigid construction to withstand thermal and mechanical distortions.

• It should have sufficient support for the piston pin.

Thermal and Geometric Properties

Aluminum Alloy

It is important to calculate the piston temperature distribution in order to control the thermal stresses and

deformations within acceptable levels. The temperature distribution enables us to optimize the thermal aspects of the piston

design at lower cost, before the first prototype is constructed. As much as 60% of the total engine mechanical power lost is

generated by piston ring assembly. The piston skirt surface slides on the cylinder bore. A lubricant film fills the clearance

between the surfaces.

The small values of the clearance increase the frictional losses and the high values increase the secondary motion

of the piston. Most of the Internal Combustion (IC) engine pistons are made of an aluminum alloy which has a thermal

expansion coefficient, 80% higher than the cylinder bore material made of cast iron. This leads to some differences

between running and the design clearances.

Therefore, analysis of the piston thermal behaviour is extremely crucial in designing more efficient engine [5].

The thermal and geometric properties are as shown in below table 2

Linear Static Structural Analysis of Optimized Piston for Bio-Fuel Using ANSYS 13

Table 1: Thermal and Geometric Properties

S.No. Name of the Property Value

1 Thermal conductivity 174.15 W/mK

2 Specific Heat 0.13 J/kgK

3 Young’s Modulus 71e3 Mpa

4 Poisson’s Ratio 0.33

5 Density, Dens 2.77e-6 kg/mm³

OPTIMIZATION

After generating an accurate finite element model a strategy for the optimization workflow was defined. Target of

the optimization was to reach a mass reduction of the piston [6].

Objective Function

Minimize mass

Subject to Constraints

• Maximum Vonmises stress<Allowable or design stress

• Factor of safety>1.2

• Manufacturing constraints

• After carrying out static structural analysis the stresses in each loading conditions were studied and then area

where excess material can be removed were decided so that maximum vonmises stress does not exceed allowable

and factor of safety is kept above 1.5 .

• Following reasons where scope for material removal

• Radial Thickness of the ring

• Axial Thickness of the ring

• Maximum Thickness of the Barrel

• Width of the Top Land

• Width of other ring lands

The Piston Model before Optimization

The following are the sequence of steps in which the piston is modeled.

• Drawing a half portion of piston

• Exiting the sketcher

• Developing the model

• Creating a hole

• Applying fillets


Piston was modeled using CATIA V5 software which is shown in Figure 1

Figure 1: Piston before Optimization

It was then imported to ANSYS 11.0. for analysis and optimization. Specifications of piston before optimization

are shown in Table 2.

Table 2: Design Specification before Optimization

S.No. Dimensions Size in mm

1 Length of the Piston(L) 152

2 Cylinder bore/outside diameter of the piston(D) 140

3 Thickness of piston head (tH) 9.036

4 Radial thickness of the ring (t1) 5.24

5 Axial thickness of the ring (t2) 5

6 Width of the top land (b1) 10

7 Width of other ring lands (b2) 4

The Piston Model after Optimization

The optimized model of the piston is as shown in below Figure 2.

Figure 2: Piston after Optimization


The model of the piston as shown in Figure 3.

Figure 3: Model of the Piston

The optimized values after optimization using ANSYS are given in the following Table 3

Table 3: Design Values after Optimization

S.

No. Parameter

Before

Optimization

After

Optimization

Design

Consideration

1 Volume 997021 mm³ 752994mm³ 752994mm3

2 Radial thickness of the ring (t1) 5.24 mm 3.46 mm 4 mm

3 Axial thickness of the ring (t2) 5 mm 3.52 mm 4 mm

4 Maximum Thickness of Barrel (t3) 14.34 mm 9.08 mm 10 mm

5 Width of the top land (b1) 10.84 mm 9.36 mm 10 mm

6 Width of other ring lands (b2) 4 mm 3.24 mm 3 mm

7 Von mises stress 63.019Mpa 75.95Mpa 63-76Mpa

8 Deflection 0.0198 mm 0.120mm 0.120mm

After obtaining the optimized piston [7], it had undergone the linear static structural analysis.

Coated Piston Materials

The piston is coated with zirconium and the details of material are as follows:

Conventional metals and lubricants fail to perform at elevated temperatures, advanced ceramic materials such as

nitrides and carbides of silicon(Si2N4 and SiC); oxides of chromium, aluminum, and iron(Cr2O3, Al2O3 and FeO2); and

partially stabilized oxide of zirconium ( ZrO2 or PSZ)] provide an alternative, Low ductility, low tensile strength, and low

bending strength have impeded the direct replacement of metals with ceramics in conventional engine designs. A high

temperature resistant coating has recently been developed with main objective to provide thermal insulation to metallic

components at elevated temperature especially for diesel, gas turbine and aero-engine applications [8]. The zirconium

coating is applied on head of the optimized piston with 140mm diameter and 0.005mm thickness. This coating process and

analysis is performed in ANSYS Workbench. The properties of material as follows

Table 4: Thermal and Geometric Properties of Zirconium

S.No. Name of the Property Value

1 Thermal conductivity 7.32 W/mm·°C

2 Specific Heat 2.19 J/kg·°C

3 Young’s Modulus 2.2e5 Mpa

4 Poisson’s Ratio 0.31

5 Density, Dens 5.5e-7kg/mm³


The Figure 4 shows coated piston and Figure 5 shows fixing of Body-to-Ground at gudgeon pin hole.

Figure 4: Coated Piston

Figure 5: Fixing of Body-to-Ground at Gudgeon Pin Hole

RESULTS AND DISCUSSIONS

The following images are shown for resulted vonmisses stresses before and after optimization

Figure 6: Vonmisses Stress before Optimization

Figure 7: Vonmisses Stress after Optimization


The optimized values after optimization using ANSYS are given in the following Table 5

Table 5: Design Values after Optimization

S.No. Parameter Before

Optimization

After

Optimization

Design

Consideration

1 Volume 997021 mm³ 752994mm³ 752994mm3

2 Radial thickness of the ring (t1) 5.24 mm 3.46 mm 4 mm

3 Axial thickness of the ring (t2) 5 mm 3.52 mm 4 mm

4 Maximum Thickness of Barrel (t3) 14.34 mm 9.08 mm 10 mm

5 Width of the top land (b1) 10.84 mm 9.36 mm 10 mm

6 Width of other ring lands (b2) 4 mm 3.24 mm 3 mm

7 Von mises stress 63.019Mpa 75.95Mpa 63-76Mpa

8 Deflection 0.0198 mm 0.120mm 0.120mm

The length 152mm of the piston obtained is same as before and after optimization process. The value after

optimization is taken into consideration. It is not considerable that the variations in piston length. Applying the temperature

and pressure loads on different areas of the piston and heat flow has not affected the length.

The diameter also same even after optimization process i.e., 140mm and is taken into consideration for design

purposes. The heat flow in the piston material and pressure on the head has not affected in length and diameter as these are

larger than other parameters. So the piston can withstand easily on sizes of these parameters.

The volume has varied after applying temperature and pressure loads over the piston as volume is depends on not

only on length and diameter and also on thicknesses. The volumetric size after optimization is taken into consideration.

The volume of piston before optimization is 997021 mm³ and for the same after optimization is 752994mm³

The radial thickness of the piston has affected more as it is very small in size and the temperature and heat flow

are very high to this size of thickness. Before optimization value is given as 5.24mm and obtained after optimization is

3.46mm. This is rounded to next highest value i.e., 4mm and is taken into consideration for design. The axial thickness of

the piston ring before optimization is 5mm, it is changed to 3.52mm after optimization, since the more and more heat and

stress applied through groves as it is very near to the head of the piston. This is rounded to next highest value i.e., 4mm is

taken into consideration for design.

The maximum thickness of the barrel before optimization is 14.34mm has much affected in variation of size after

applying pressure and temperature loads and is changed to 9.08mm and rounded to next highest value i.e., 10mm taken

into consideration.

The width of the top land has not much affected while comparing with the maximum thickness of the barrel. The

initial value i.e., before optimization is 10.84mm and is changed after applying pressure which is directly applied on the

head i.e., top of the piston as a result the shape of the piston on top will become just like a bowl. The value after

optimization is obtained as 9.36mm and it is rounded to 10mm. This value is considerable for design.

The width of the other lands i.e., near piston rings are 4mm in size and is changed due to pressure and heat applied

on rings through groves. The value after optimization is 3.24mm and is rounded to 3mm.

The von misses stress initially was 63.019Mpa, after optimization it is obtained as 75.95Mpa and it is permissible

up to 90Mpa. So the piston with these considerations can withstand easily.


The deflection due to pressure applied is more than that of temperature applied. In this analysis the pressure as

well as temperature loads are taken into consideration for applying on the piston. The deflection before optimization is

given as 0.0198mm and after optimization it is obtained that 0.120mm, this value is taken into consideration for design

purpose.

The values obtained after applying the loads are depend on the area chosen by the user. The factor of safety is as

follows:

• The mass of the piston before optimization is 2.72. and factor of safety of is 1.42

• The mass of the piston after optimization is 2.08. and factor of safety of is 1.2

Linear Static Structural Analysis and Images of Coated Piston

The Optimized Piston is coated with Zirconium surface body of 0.005mm thickness. The images are as follows;

Von Misses Stress of Coated Piston

Figure 8: Linear Static Structural Analysis - Von Mises Stress of Coated Piston

Deformation of Coated Piston

Figure 9: Linear Static Structural Analysis - Deformation of Coated Piston

The following tables shows the parameter details of linear static structural analysis

Table 6: Vonmisses Stress and Deflection Parameters of Linear Static Structural Analysis

S.No. Parameter After Optimization Coated Piston Design Consideration

1 Von mises stress 74.95Mpa 78.489Mpa 74-84 Mpa

2 Deflection 0.120mm 0.0407mm 0.0407mm


The vonmisses stress initially was i.e., for optimized conventional piston is 74.95Mpa after coating the von-Mises

Stress is obtained as 78.489Mpa and it is permissible up to 90Mpa. So the piston with these considerations can withstand

easily and is under linear control.

The deflection due to pressure applied is more than that of temperature applied. In this analysis the pressure as

well as temperature loads are taken into consideration for applying on the piston. The deflection after optimization is given

as 0.120mm and same for coated piston is obtained that 0.0407mm, this value is taken into consideration for design

purpose.

CONCLUSIONS

The deflection due to pressure applied after optimization is more than before optimization and this value is taken

into consideration for design purpose. The stress distribution on the piston mainly depends on the deformation of piston.

Therefore, in order to reduce the stress concentration, the piston crown should have enough stiffness to reduce the

deformation.

All the phases in this project given can be extended to the piston design with reduction of material at bottom. The

material is removed to reduce the weight of the piston so as to improve the efficiency. It is essential to obtain the optimized

results for new piston with reduced material.

In brief

• The optimal mathematical model which includes formation of piston crown and quality of piston ad piston skirt.

• The FEA is carried out for standard piston model used in diesel engine ceramic coating on crown and the result of

analysis indicate that the maximum stress has changed from 63.019Mpa to 74.95Mpa.

The zirconium coated piston also obtained with the parameters, stress for given pressure and are within the

permissible values. The coated piston is useful for bio-fuel. The same design, analysis can be extended to connecting rod,

other parts of the engine and different coated pistons. The variational properties, which are applied on piston, can also be

analyzed with the same approach for optimistic design. The different material can be used for piston for which the same

analysis can extended.

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2.Mech - IJMPERD - Linear Static - P.v.K

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